Agreed. I have the Salamander Synergy 40/20 for my secondary system and it is just fine. It all comes to about 400-500lbs. But I am keeping the power amp on the bottom of the bottom module and the UPS/line controller on the bottom of the top module so that both are on 1.5 shelves which are supported by the extrusions, not the shelf brackets.
If you have 800-1000lbs, I'd go with steel-frame and fixed shelves.
If you have 800-1000lbs, I'd go with steel-frame and fixed shelves.